Tank Inspection Report Town of Christiansburg, VA Hills Tank Liquid Engineering Corporation 36903

Transcription

1 Tank Inspection Report Liquid Engineering Corporation GENERAL Tank Name: Type: On-Grade Standpipe City: Christiansburg Tank Capacity: 500,000 Gallon State: Virginia Type of Construction: Welded Steel Year Built: unknown Inspected By: LEC Maintenance Team 13 Team Leader Benavente Inspection Date: May 16, 2009 This report is a supplement to the visual and video inspection undertaken for the Town of Christiansburg, by Liquid Engineering Corporation of Billings, MT. The is an on-grade (standpipe) water storage tank. (See Photo No.1). The tank has a 500,000-gallon capacity with an overall height of 65 and an overall diameter of 38. The tank is founded on a concrete base. Photograph No. 1

2 STANDARDS The inspection of this tank was performed by a dive maintenance technician using surface supplied air, totally encapsulated in a sealed dry suit mated to a sealed dry divers hard hat and conducted in accordance with all applicable OSHA, EPA, AWWA, NACE, SSPC and ADC requirements and/or recommendations. The inspection consisted of a visual observation of the tank s interior and exterior components and coating system. The tank was not drained for the inspection and all interior assessment data was recorded using real time video with live voice narration. Exterior assessment data was documented using digital still photographs. CONDITION OBSERVATIONS Conditions noted during the field inspection are documented in the following pages and are supplemented with color photographs at the end of the report. Condition ratings used to describe the inspection findings are annotated as follows: Excellent: Good: Fair: Poor: No deficiencies noted. Minor deficiencies noted. Item is functioning as designed. Major deficiencies noted. Item is in need of repairs to continue functioning as designed. Repair or replacement required immediately. Item may no longer function as designed. CONTAMINATION, HEALTH & SAFETY REPORT Contamination and Health Air Vent(s) and Screen(s) There is one mushroom style air vent in the center roof of the tank. The vent appears to be secure, screened, and in Good condition. Hatches The rectangular roof hatch appears to be secure and properly sealed, and exhibits a Fair condition. Heavy uniform surface corrosion, concentration cell corrosion, and dealloying is present on the edges of the appurtenance. There is a second hatch displaying the same condition as described above. Exterior Overflow The exterior overflow shows no flapper valve or gasket, but appears to be properly screened. No major discrepancies are noted at this time. Cathodic Covers N/A, there is no cathodic protection system in this reservoir. Roof to Wall Joint The welded joint appears to be secure and sealed properly, with no visible light penetration. Roof Integrity No holes or standing water stains were noted at the time of inspection. Wall Integrity No holes were visible on the walls. The walls show no visible deformity. Manway Integrity The manway shows no visible leaking; proper gasket material is in place. Water Clarity - Good and no floating surface debris was noted. Telemetry Penetration(s) The telemetry penetration appears to be sealed properly at this time. Facility Safety Compliance External Ladder - All attachments and rungs appear to be secure and in Good condition. There is a locking vandal guard present, which was intact at the time of inspection. Ladder Rails and Rung(s) The rung spacing is 12, the toe depth measures 8 ½, the rail width is 2, rail thickness of ½, and the rail to rail span measures 14. Safety Climb - There is a cage type safety climb system present on the exterior ladder. All safety climb components appear to be functional and in Good condition. Manway There is one 34 diameter manway bolted to the tank shell. The manway structure appears to be sealed properly with adequate gasket material in place. Hatch - The rectangular roof hatch measures 32 x 28, with a 8 ½ lip height and a 2 lid overlap. Balcony & Railing N/A, there is no balcony or railing on this tank roof. OSHA fall protection guidelines recommend a safety rail be present consisting of a minimum 42 handrail, two rails and a 4 toe rail. Roof The roof area only has 2 safety tie off points. Installation of additional tie off points is recommended to assist in safe access of the roof area. There are 2 antennas on the roof as well.

3 INTERIOR RESERVOIR INSPECTION REPORT Interior Reservoir Roof Vent(s) The interior portion of the vent was not visible due to the construction of the roof bracing structure. Condensation was noted to be heavy on the interior roof panels, which indicates inadequate ventilation. Installation of a larger or secondary vent is recommended to alleviate the humidity from the tank roof. Roof Panels The roof panels appear to be secure and sound, but corrosion was identified on all roof panels. Approximately 3% of the roof area is noted to show some form of corrosion. The interior roof panels show uniform surface corrosion and dealloying, mainly located on the roof to wall weld and panel weld seams, but the panels are currently rated in Good condition. Roof Support Structure The roof support structure is rated in Fair condition, as uniform surface corrosion and dealloying is present across the entire area. The area rates a 3 on the SSPC legend, with approximately 17% of the surface area being corroded. Roof Support Gussets The roof support gussets show a similar amount of corrosion as the roof support structure, with 17% of the surface area being rusted. Protective Coating The protective coating appears to be in Fair condition. The penetrating corrosion is mainly located on the roof to wall weld and gusset junctions. The coating shows staining and the corrosion is evidence of coating breakdown. Interior Reservoir Walls Wall to Roof Weld The weld appears to be intact with no visible light penetration, but the weld is showing 100% surface corrosion with dealloying. There are isolated areas of corrosion staining falling onto the wall panels. The weld should be considered in Poor condition. Ring Panels The interior ring panels show numerous areas of concentration cell corrosion, as well as uniform surface corrosion and pitting. The upper ring panels show the most concentration of corrosion present. The upper ring panels rate a 5 on the SSPC code, with 3% of the surface area showing corrosion. The middle and lower panels show a slightly better rating, with approximately 0.3%. The average pit depth is 1/16 th. At a minimum, it is recommended that the pits be prepped and coated with an NSF approved epoxy to prevent further degradation of the steel substrate. A blast and recoat of the surface should be considered in the next few years. Painter s Ring The underside of the painter s ring shows heavy concentration cell corrosion and dealloying. Interior Ladder The interior ladder and standoffs appear to be in Good condition, although concentration cell corrosion is prevalent across the appurtenance edges, rungs, and rails. Protective Coating The protective coating appears to be in Fair condition. Isolated areas of heavy blistering were noted in these areas. The ring panel coating shows heavy discrepancy including blistering with checks and cracks, delamination and heavy corrosion staining across the coating surface, as well as pinholes and the corrosion penetrating in isolated areas. Average blister is ¼ in diameter. Installation of a cathodic protection system is recommended to suppress the spread of corrosion and extend the useful life of the tank s steel makeup. Interior Reservoir Floor Perimeter Weld The weld could not be fully examined due to the presence of the floor sediment. Areas of concentration cell corrosion were identified protruding the sediment layer. Floor Panels The floor panels were not able to be evaluated due to the sediment layer present on the floor panels. The sediment layer averaged 1/8 deep in all areas. Concentration cell corrosion was visible on the floor panels through the sediment layer. It is recommended that the town utilize Liquid Engineering s In- Service cleaning method to remove the sediment layer and fully evaluate the floor panels, as additional corrosion may be present but not viewable due to the sediment layer. Protective Coating - The protective coating could not be fully evaluated due to the presence of sediment on the tank floor.

4 INTERIOR RESERVOIR INSPECTION REPORT contd. Interior Reservoir Support Columns Column Structure(s) The interior column shows similar conditions as the wall panels, with higher discrepancies noted on the upper portions (dealloying and uniform surface corrosion). Column Base Structure The column base structure shows minor uniform surface corrosion, staining, as well as isolated concentration cell corrosion near the edges. Some of the base was not fully evaluated due to the presence of the sediment layer on the floor. Column to Roof Structure The column to roof area shows the highest level of discrepancy on the column. Heavy uniform surface corrosion and dealloying is present in this area. See coating condition below. Protective Coating The protective coating appears to be in Fair condition. The middle and lower portion shows little discrepancy, but blistering and delamination was found on the upper portion of the column. The utility should consider touching up the affected areas with an NSF approved epoxy. Average blister size is ¼ in diameter. Interior Reservoir Plumbing Components Inlet Plumbing The inlet is located in Quadrant 1 and shows moderate concentration cell and uniform surface corrosion. The inlet structure exhibits a Fair condition. The inspector rates the corrosion a 2 on the SSPC chart, with approximately 33% of the area corroded. Corrosion removal with an NSF epoxy touch up is recommended to halt the further spread of corrosion. Outlet Plumbing The outlet appurtenance located in Quadrant 4 also shows a similar condition as the inlet. Concentration cell corrosion is present on the interior and edge portions. The similar corrosion removal and touch up is also recommended. Manways The coating shows staining and blistering, with average blister size of ¼ in diameter. The manway shows adequate gasket material present, with concentration cell corrosion around the edges. Floor Drains N/A, no floor drain was identified in this tank. Overflow The interior overflow penetrates the upper wall in Quadrant 1. The plumbing penetration shows uniform surface corrosion, but the plumbing exhibits a Good condition. EXTERIOR RESERVOIR INSPECTION REPORT Exterior Reservoir Roof Vent(s) The center roof vent contains a fine mesh screen. All components are intact and the vent is rated in Good condition. The vent is corroded to the extent of 1% of the surface area, including the interior screen. Roof Panels All roof panels appear to be in Fair condition, as heavy uniform surface corrosion is present across the entire roof area. The panels show no visible deformity. It is recommended that the roof be touched up in every area of discrepancy at a minimum, with a full prep/recoat of the area encouraged. Access Hatch The access hatch has evidence of dealloying and concentration cell corrosion on the edges of the structure. Corrosion removal and full touch up of the area is recommended to stop the advancement of the corrosion. The coating on the hatch shows heavy delamination. Protective Coating - The coating on the roof panels shows chalking, scratches, staining, and delamination. Uniform surface corrosion is present on the exposed steel substrate. Touch up or a full prep/recoat is recommended of roof coating. Exterior Reservoir Walls Wall to Roof Weld The wall to roof weld appears secure and sealed properly from the exterior. Uniform surface corrosion is present. (See also Interior Reservoir Walls Wall to Roof Weld) Ring Panels All wall panels appear to be in Fair condition. The inspector noted sporadic areas of coating failure with uniform surface corrosion forming on the exposed steel substrate. The inspector did not observe any signs of deformity in the ring panels. Overflow The overflow shows evidence of uniform surface corrosion, however; it appears to be in Good condition.

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6 APPENDIX A Photographs

7 Interior floor outlet Interior floor inlet

8 Interior wall panel (note areas of concentration cell corrosion and primer visible through coating) Interior column base (note evidence of delaminated coating in the sediment)

9 Interior upper column (note coating delamination) Average size of typical concentration cell corrosion

10 Interior painter s ring (note heavy concentration cell corrosion on underside) Exterior view of shell manway (note surrounding areas of coating delamination and corrosion)

11 Exterior concrete foundation (note minor cracking) Exterior ladder and water level gauge board

12 Exterior view of roof hatch (note coating delamination and heavy dealloying and surface corrosion) Exterior view of center roof vent (note scratches in coating and surrounding surface corrosion)

13 Exterior roof view (note heavy surface corrosion) Exterior view of roof panels (note heavy uniform surface corrosion and coating scratches)

14 APPENDIX B Field Notes

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